1. Field of the Invention
The present invention generally relates to plunger lift technology and, more particular, is concerned with a plunger arrival target time adjustment method using both A and B valve open times.
2. Description of the Prior Art
In a typical prior art plunger lift system, such as seen in FIG. 1, a gas-producing well W employs a freely movable plunger P disposed within a tubing string T in the well that is capable of traveling vertically in the tubing string T as the well W is cycled between shut-in and open conditions. The well W is shut-in for an interval during which the pressure of gas G gradually elevates within the well casing C. When the pressure of gas G reaches a desired level, a master gas flow control valve A, commonly referred to as the A valve, is opened causing the plunger P to be propelled by the accumulated gas pressure from a lower initial position, at a bottom bumper B, upward in the tubing string T toward an upper terminal position adjacent to a plunger arrival sensor S. Liquid, such as water F, and gas G above the plunger P discharges from the well W through a horizontal conduit H into a flow line L, called a gas sales line, leading to a separator (not shown). At the separator, gas and water separate from one another and are routed to separate storage vessels. The plunger P is held at the upper terminal position until the gas pressure diminishes to an extent permitting the plunger P to fall under gravity to its lower initial position.
Many plunger lift systems, in addition to the master flow control or A valve, will typically utilize a second flow control valve, commonly referred to in the industry as the B valve and an electronic controller E to control cycling of the well between shut-in and open times and thereby the production of gas from the well. As mentioned above, the A valve is interposed in the gas sales line L. The B valve is interposed in a vent line that leads to a containment tank or pit or sometimes directly to atmosphere. The gas sales line L is under a higher pressure than the vent line. The shut-in and open times of the cycles providing optimum well production will vary from well to well. The electronic controller E is programmed to set and control the times of opening and closing of the A and B valves as well as other functions to provide for optimum production at a given well. Also, the plunger lift system typically employs the arrival sensor S at the wellhead to sense the arrival of the plunger P at the upper terminal position. The arrival sensor S sends an electrical signal to the electronic controller E in response to the arrival of the plunger P.
The employment of the B valve is necessary on many wells due to pressure fluctuations experienced in the high pressure gas sales line L of such wells which can impede efficient production of gas G from the well W. There are various causes of pressure variation, the main ones being conditions created by mechanical equipment attached to the gas sales line L or the weather. When gas sales line pressure fluctuates enough that it becomes too great for the well casing pressure to exceed it and drive the plunger P to the upper terminal position of the wellhead, the plunger P may stall before reaching the surface or not arrive at the upper terminal position within the preset open time of the A valve. The electronic controller E is programmed to then close the A valve and open the B valve to vent the well casing C to atmosphere or a low pressure tank or pit and thereby permit the plunger P to reach the upper terminal position and blow out the fluid that has accumulated above the plunger P. After the plunger P arrives and blows out the fluid, the electronic controller E will shut the B valve and open the A valve and thus commence sale of gas from the well W through the A valve and the gas sales line L.
Heretofore, electronic controllers have been programmed to set an initial A-valve open time and then to adjust the A-valve open time in order to reach a time value which optimizes production and sales of gas from the well. These adjustments are made by the electronic controller following a programmed sequence of steps that use only the past consecutive readings of the plunger arrival times which fall during A-valve open times. In some instances it may take the electronic controller from a few hours to many days to make the incremental changes necessary to optimize well shut-in and open cycle times for optimized production and sales of gas from the well. Should the plunger P fail just once to arrive at the upper terminal position of the wellhead within the assigned A-valve open time as the electronic controller is proceeding through its programmed optimization sequence or after completion thereof, the electronic controller is programmed to treat this event as a plunger arrival failure even through the plunger does subsequently arrive during the B-valve open time after the system has closed the A valve and opened the B valve.
In response to the noted plunger arrival failure, the electronic controller is programmed to return to its initial preset or programmed A-valve open time and begin the programmed optimization sequence over again. This results in a loss of the time, in terms of hours or days, which was spent to reach the optimized A-valve open time in the first place which adversely affects the efficiency of gas production and sales being made from the well.
Consequently, a need exists for improvement of the programmed optimization sequence for setting A-valve open time to improve control of cycling of the well between shut-in and open times and thereby improve the efficiency of gas production and sales from the well.